Patent application title: Coated cermet cutting tool and use thereof

Abstract:

A cutting tool insert has a cermet body with a Co and/or Ni binder phase
and a coating deposited as monolayer or as multiple and/or alternating
layers of carbide, nitride or oxide. The coating has a thickness of 21-50
μm, when the inserts have a flat rake face, without or with simple
chipbreakers and a Co binder phase, or has a thickness of 10-50 μm,
when the inserts have a rake face land with a width of 100-300 μm with
an angle of 10-25° to the rake face and a Co and/or Ni binder
phase. The cermet body has more than 50 vol. % Ti-based carbonitride and
less than 15 wt % and more than 6 wt % Co and/or Ni binder phase and a
hardness of >1650 HV3. The disclosure also relates to the use of the
coated cutting tool insert for the machining of cast iron work pieces.

Claims:

1. A cutting tool insert comprising:a cermet body including a Co and/or Ni
binder phase; anda coating deposited as a monolayer or as multiple and/or
alternating layers of carbide, nitride or oxide deposited by CVD- and/or
MTCVD-methods,wherein said cermet body includes more than 50 vol. %
Ti-based carbonitride and less than 15 wt. % but more than 6 wt. % Co
and/or Ni binder phase,wherein said cermet body has a hardness, measured
as Vickers Hardness at 3 kg load (HV3), of >1650 HV3, andwherein said
coating has:(a) a thickness of 21-50 μm when the inserts have a flat
rake face, without or with simple chipbreakers and a Co binder phase,
or(b) a thickness of 10-50 μm when the inserts have a rake face land
with a width of 100-300 μm with an angle of 10-25.degree. to the rake
face and a Co and/or Ni binder phase.

2. The cutting tool insert according to claim 1, wherein the grain size of
the Ti-based carbonitride phase is 0.5-4 μm.

3. The cutting tool insert according to claim 1, wherein the coating
comprises at least one layer of a carbide, carbonitride or carboxynitride
of one or more of Ti, Zr and Hf or mixtures thereof and at least one
layer of alumina.

4. The cutting tool insert according to claim 3, wherein the coating
includes a top layer of TiN with a thickness of <2 μm.

5. The cutting tool insert according to claim 4, wherein the TiN is an
outermost layer on the clearance faces and the alumina is an outermost
layer on the rake face.

6. The cutting tool insert according to claim 3, wherein the coating
comprises a first layer adjacent to the cermet body with a thickness of
more than 6 μm but less than 45 μm including at least one of
carbide, nitride, carbonitride or carboxynitride of one or more of Ti, Zr
and Hf or mixtures thereof and a second α-Al2O3-layer
adjacent to the first layer with a thickness of more than 4 μm but
less than 44 μm.

7. The cutting tool insert according to claim 6, wherein the thickness of
the first layer is more than 10 μm.

8. The cutting tool insert according to claim 6, wherein the thickness of
the second α-Al2O3-layer is more than 15 μm.

9. The cutting tool insert according to claim 6, wherein the first layer
comprises Ti(C,N).

10. The cutting tool insert according to claim 3, wherein the coating
comprises:a first layer adjacent the cermet body, the first layer
including a carbide, nitride, carbonitride or carboxynitride of Ti, or Zr
or Hf with a thickness of 6-30 μm;an α-alumina layer adjacent
said first layer with a thickness of 5-50 μm;a further layer adjacent
the alumina layer, the further layer including a carbide, carbonitride or
carboxynitride of one or more of the metals Ti, Zr and Hf or mixtures
thereof with a thickness of 5-30 μm; anda further α-alumina
layer adjacent said further layer with a thickness of 5-30 μm.

11. The cutting tool insert according to claim 10, wherein the coating
includes a top layer of TiN with a thickness of <2 μm.

12. The cutting tool insert according to claim 11, wherein the TiN-layer
is an outermost layer on the clearance faces and the alumina is an
outermost layer on the rake face.

13. The cutting tool insert according to claim 1, wherein the hardness of
said cermet body is >1750 HV3.

14. The cutting tool insert according to claim 13, wherein the hardness of
said cermet body is >1775 HV3.

15. The cutting tool insert according to claim 1, wherein the thickness of
the coating is 25-50 μm when the inserts have a flat rake face,
without or with simple chipbreakers and a Co binder phase.

16. The cutting tool insert according to claim 15, wherein the thickness
of the coating is 30-50 μm when the inserts have a flat rake face,
without or with simple chipbreakers and a Co binder phase.

17. The cutting tool insert according to claim 16, wherein the thickness
of the coating is 35-50 μm when the inserts have a flat rake face,
without or with simple chipbreakers and a Co binder phase.

18. The cutting tool insert according to claim 1, wherein the thickness of
the coating is 15-50 μm when the inserts have a rake face land with a
width of 100-300 μm with an angle of 10-25.degree. to the rake face
and a Co and/or Ni binder phase.

19. The cutting tool insert according to claim 18, wherein the thickness
of the coating is 21-50 μm when the inserts have a rake face land with
a width of 100-300 μm with an angle of 10-25.degree. to the rake face
and a Co and/or Ni binder phase.

20. The cutting tool insert according to claim 19, wherein the thickness
of the coating is 30-50 μm when the inserts have a rake face land with
a width of 100-300 μm with an angle of 10-25.degree. to the rake face
and a Co and/or Ni binder phase.

21. The use of a coated cutting tool insert according to claim 1 for the
machining of cast iron workpieces at a cutting speed of >300 m/min at
a cutting depth of 2-8 mm and a feed rate of 0.2-0.7 mm/rev.

22. The use of a coated cutting tool insert according to claim 21, wherein
the cutting speed is 400-1000 m/min.

23. A method of machining a workpiece, comprising removing material from
the workpiece with the cutting tool insert according to claim 1, wherein
the cutting tool operates at a cutting speed of >300 m/min at a
cutting depth of 2-8 mm and a feed rate of 0.2-0.7 mm/rev and wherein the
workpiece is nodular cast iron (NCI), compact graphite iron (CGI) or grey
cast iron (GCI).

[0002]In the discussion of the background that follows, reference is made
to certain structures and/or methods. However, the following references
should not be construed as an admission that these structures and/or
methods constitute prior art. Applicants expressly reserve the right to
demonstrate that such structures and/or methods do not qualify as prior
art.

[0003]Cermets tools are used with good results in finishing operations of
steel but, due to their brittleness, cermets tools are not used in high
productivity machining operations together with large cutting depths and
large feeds requiring increased toughness. In addition, cermets tools are
not used in machining of cast irons, especially not in medium to roughing
operations.

[0004]The various cast iron grades are machined with use of chemical vapor
deposition (CVD) coated cemented carbide cutting tool inserts. Grey cast
iron is also machined with silicon nitride based ceramic cutting tools.
However ceramic tools are expensive because of the high manufacturing
cost. It is therefore a desire, if possible, to replace ceramic tools
with less expensive tools. The ceramic tools, such as based on silicon
nitride, perform well in grey cast iron, however, show limited tool life
in nodular cast iron. Thus, conventional coated cemented carbide tools
are used in nodular cast iron area.

[0005]However, there are demands from various machining industries for
tools with higher productivity and longer tool life than that obtained by
conventional coated cemented carbide.

[0006]Cemented carbide cutting tools coated with various types of hard CVD
layers have been commercially available for years. Such tool coatings are
generally built up by one Ti(C,N) and one Al2O3 hard layer
where the Ti(C,N) is the innermost layer adjacent to the cemented
carbide. The thickness of the individual layers is carefully chosen to
suit different cutting applications and work-piece materials, e.g., cast
iron and various steel grades. Coated cemented carbide tool inserts may
be used for both continuous and interrupted cutting operations of various
types of steels and cast irons.

[0008]U.S. Pat. No. 6,183,846 disclose a coated cutting tool including a
hard coating on a surface of a base material of cemented carbide or
cermet. The hard coating includes an inner layer on the base material, an
intermediate layer on the inner layer and an outer layer on the
intermediate layer. The inner layer with a thickness of 0.1 to 5 μm
consists of a carbide, a nitride, a carbonitride, a carbooxide, a
carboxinitride or a boronitride of Ti. The intermediate layer consists of
Al2O3 with a thickness of 5 to 50 μm or ZrO2 with a
thickness of 0.5 to 20 μm. The outer layer with a thickness of 5 to
100 μm consists of a carbide, a nitride, a carbonitride, a
carbo-oxide, a carboxinitride or a boronitride of Ti.

[0009]EP 1643012A discloses a method for high speed machining of a
metallic work piece at a cutting speed of 800-1500 m/min, a cutting depth
of 2-4 mm, and a feed rate of 0.3-0.7 mm/rev with a coated cemented
carbide cutting tool. The cutting tool comprises a coating as a monolayer
or multiple layers with a total thickness of 25-75 μm and a cemented
carbide body with hardness of >1600 HV3, preferably over 1700 HV3. The
best results are obtained in machining of grey cast iron.

SUMMARY

[0010]It is therefore an object of the present disclosure to provide a
cutting tool insert excellent in high efficiency cutting of nodular cast
iron (NCI) and compact graphite iron (CGI).

[0011]It has now surprisingly been found that a cutting tool insert
comprising a thick coating and a cermet body is excellent in high
efficiency cutting of various cast irons, such as nodular cast iron
(NCI), compact graphite iron (CGI) and grey cast iron (GCI), preferably
machining of nodular cast iron (NCI) and compact graphite cast iron
(CGI). The coating is deposited using conventional CVD or
MT-CVD-techniques known in the art.

[0012]An exemplary cutting tool insert comprises a cermet body including a
Co and/or Ni binder phase, and a coating deposited as a monolayer or as
multiple and/or alternating layers of carbide, nitride or oxide deposited
by CVD- and/or MTCVD-methods, wherein said cermet body includes more than
50 vol. % Ti-based carbonitride and less than 15 wt. % but more than 6
wt. % Co and/or Ni binder phase, wherein said cermet body has a hardness,
measured as Vickers Hardness at 3 kg load (HV3), of >1650 HV3, and
wherein said coating has one of (a) a thickness of 21-50 μm when the
inserts have a flat rake face, without or with simple chipbreakers and a
Co binder phase, or (b) a thickness of 10-50 μm when the inserts have
a rake face land with a width of 100-300 μm with an angle of
10-25° to the rake face and a Co and/or Ni binder phase.

[0013]An exemplary method of use and an exemplary method of machining a
workpiece are also disclosed.

[0014]It is to be understood that both the foregoing general description
and the following detailed description are exemplary and explanatory and
are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWING

[0015]The following detailed description can be read in connection with
the accompanying drawings in which like numerals designate like elements
and in which:

[0016]FIG. 1 shows an edge of an insert in cross section provided with a
coating.

[0020]The present disclosure relates to a cutting tool insert comprising a
cermet body comprising Ti-based carbonitride in a Co and/or Ni binder
phase and a coating deposited as a monolayer or as multiple and/or
alternating layers of carbide, nitride or oxide or solid solutions or
mixtures thereof, by CVD- and/or MTCVD-methods. The coating has a
thickness of 21-50 μm, preferably 25-50 μm, more preferably 30-50
μm and most preferably 35-50 μm when the inserts have a flat rake
face, with or without simple chipbreakers, with a Co-binder phase or a
thickness of 10-50 μm, preferably 15-50 μm, more preferably 21-50
μm and most preferably 30-50 μm, when the inserts have a rake face
land with a width of 100-300 μm with an angle of 10-25° to the
rake face with a Co and/or Ni binder phase.

[0021]The cermet insert body consists of a conventional cermet body based,
more than 50 vol. %, on a cubic Ti-based carbonitride phase and a binder
phase of Co and/or Ni, preferably Co, and at least one of W or Mo.
Further elements, which may be present in the cermet body, are those
conventionally used in cermet cutting tools such as Ta, Nb, V, Zr, Hf,
Cr. The binder phase content is less than 15 wt. %, preferably less than
13 wt. %, most preferably less than 10 wt. %, but more than 6.0 wt. %.
The grain size of the Ti-comprising carbonitride phase is 0.5-4 μm,
preferably 1-3 μm. The cermet body has a hardness of >1650 HV3,
preferably >1750 HV3, most preferably >1775 HV3. Hardness HV3 means
Vickers hardness measured at 3 kg weight.

[0022]In one embodiment, the coating comprises at least one layer of a
carbide, nitride, carbonitride or carboxynitride of one or more of Ti, Zr
and Hf or mixtures thereof and at least one layer of alumina, preferably
α-alumina in any combination.

[0023]In one embodiment, the coating consists of a first layer adjacent to
the cermet body with a thickness of more than 6 μm, preferably more
than 10 μm and most preferably more than 20 μm but less than 45
μm, preferably less than 30 μm, including at least one of carbide,
nitride, carbonitride or carboxynitride of one or more of Ti, Zr and Hf
or mixtures thereof, and a second layer of Al2O3 with a
thickness of more than 4 μm, preferably more than 5 μm, most
preferably more than 15 μm but less than 44 μm, preferably less
than 25 μm, adjacent to the first layer.

[0024]In a further preferred embodiment, the coating consists of four
layers: a first layer adjacent the cermet body, the first layer including
a carbide, nitride, carbonitride or carboxynitride of one or more of Ti,
Zr and Hf or mixtures thereof with a thickness of 6-30 μm, preferably
6-15 μm, an α-alumina layer adjacent said first layer with a
thickness of 5-30 μm, preferably 5-15 μm, a further layer adjacent
the alumina layer, the further layer including a carbide, nitride,
carbonitride or carboxynitride of one or more of the metals Ti, Zr and Hf
or mixtures or multilayers thereof with a thickness of 3-30 μm,
preferably 4-15 μm, and a further α-alumina layer adjacent said
further layer with a thickness of 3-40 μm, preferably 4-20 μm.
Preferably, the first layer and/or the further layer contain Ti(C,N) with
columnar structure.

[0025]All thickness values used herein include thin conventional
transition and bonding layers or top surface layers such as TiN, Ti(C,N),
Ti(C,O), Ti(C,N,O) and Ti(N,O) and/or layers promoting adhesion and/or
phase control of a subsequently deposited layer. The thickness of these
individual layers is between 0.1 and 2 μm.

[0026]In case of the presence of Ni in the cermet body, it is suitable to
have a thin interlayer consisting of Ti(C,O) close to the cermet body,
less than 2 μm thick, in order to stop Ni diffusion into the coating.

[0027]Preferably the top layer is a 4-44 μm, preferably 5-25 μm,
thick Al2O3-layer or a <2 μm thick TiN-layer. This TiN
layer can be mechanically removed by known techniques from the rake face.
In such case, this outermost layer on the rake face is Al2O3
and on the clearance faces TiN. Mechanical removal of the TiN-layer is
performed by known methods, such as blasting treatment using hard
particles.

[0028]In some specific embodiments, one or more friction reducing
layer(s), such as layers of sulphides of tungsten and/or molybdenum, may
be applied as an outermost layer.

[0029]The present disclosure also relates to the use of a coated cutting
tool insert according to above for the machining of cast iron work
pieces, such as nodular cast iron (NCI), compact graphite iron (CGI) and
grey cast iron (GCI), at a cutting speed of >300 m/min, preferably
400-1000 m/min and most preferably 600-1000 m/min, at a cutting depth of
2-8 mm and a feed rate of 0.2-0.7 mm/rev. The size of the cutting depth
is selected with respect to the size of the cutting inserts. For smaller
inserts, the cutting depth is 2-4 mm and for larger ones 2-8 mm.

EXAMPLE 1

[0030]Cermets and cemented carbide substrates A-D with chemical
compositions according to Table 1 were produced in the conventional way
from powders, which were milled, pressed and sintered with or without
subsequent grinding to insert shapes, ISO standard CNMA120416 T02020,
CNMA120416-KR and CNMA160616 T02520 and CNMA160616-KR. Furthermore the
inserts were subjected to mechanical edge honing.

[0031]After that the inserts were cleaned and coated using processes known
in the art. Coating compositions and thicknesses appear from Table 2. Two
or four layers comprising Ti(C,N) and α-Al2O3 were
deposited. Ti(C,N) was deposited so that a columnar grain structure of
the layer was obtained. This was done by using the known MT-CVD process
(MT-medium temperature, CVD-chemical vapor deposition) where, besides
other gases, acetonitrile, CH3CN, was used as nitrogen and carbon
source. The top of alumina layer was coated with a TiN layer.

[0032]In the start of the coating process, at the transition zone between
the Ti(C,N) and Al2O3 layers and at the end of the
Al2O3 coating process, conventional processes were also used.
These conventional processes resulted in the formation of <2 μm
thick transition, bonding or outermost layers of TiN, Ti(C,O) and/or
Ti(C,N,O).

[0033]The outermost coating was a <2 μm thick TiN layer, which was
mechanically removed from the insert's rake face by known Al2O3
particle blasting technique. Thus, the outermost layer on the rake face
is Al2O3 and on the flank side is TiN. Furthermore the blasting
treatment has resulted in smoother surface topography on treated
surfaces.

[0034]Inserts of style CNMA120416 T02020, have a rake face land with a
width of 200 μm with an angle of 20° to the rake face, with an
edge honing of 30 μm (as measured on the uncoated insert) with
substrates A, B, C, D with coatings 1, 2, 3, 4, 5 designated A/1, A/2,
A/3, A/4, A5, B5, C/2, C/3, D5 were subjected to a cutting test, an
external turning operation comprising packages of 4 discs of a nodular
cast iron (NCI), comprising cast skin. The discs had a diameter of 250 mm
and they were machined down to a diameter of 120 mm by repeated passes.
The flank wear width of the cutting edge after machining 32 discs
packages was measured. As a reference was also used commercially
available Si3N4 ceramic insert with the same geometry.

[0035]Example 3 was performed with inserts A/3, A/4, C/3, D5 being
produced in the same way as that in Example 2. The insert geometry was
CNMA120416-KR, having a flat rake face, with an edge honing of 40 μm
(as measured on the uncoated insert). The cutting tests including
external turning operation in grey cast iron comprising packages of 4
discs with diameter of 250 mm, which were machined down to a diameter of
120 mm by repeated passes. The flank wear width of the cutting edge after
machining 32 discs packages was measured. As a reference was also used
commercially available Si3N4 ceramic insert with the same
geometry.

[0036]Example 4 was performed with inserts A/2, A/3, A/4, C/3, B5, D5,
being produced in the same way and having the same geometry as that in
Example 2. The cutting tests including external turning operation in
compact graphite iron (CGI) comprising packages of 4 discs with diameter
of 250 mm, which were machined down to a diameter of 120 mm by repeated
passes. The flank wear width of the cutting edge after machining 32 disc
packages was measured.

[0037]Inserts of style CNMA160616 T02520, having a rake face land with a
width of 250 μm with an angle of 20° to the rake face and an
edge honing of 30 μm (as measured on the uncoated insert), with
substrates A, B, C, D with coatings 1, 2, 3, 4, 5 designated A/2, A/3,
A/4, A5, B5, C/2, D5 were subjected to a cutting test, an external
turning operation comprising package of 4 discs of a nodular cast iron
(NCI), comprising cast skin. The discs had a diameter of 250 mm and they
were machined down to a diameter of 120 mm by repeated passes. The flank
wear width of the cutting edge after machining 48 discs packages was
measured. As a reference was also used commercially available
Si3N4 ceramic insert with the same geometry.

[0038]From Examples 2-5, it is evident that if the Co content in the
cermet body is too high, as in (D/5), plastic deformation of the cutting
edge will occur during cutting operation having negative influence on the
tool performance.

[0039]The chipping observed in Example 2, insert C/3 (prior art), having a
coating on a WC-Co based cemented carbide body is suspected to be related
to CVD-cooling cracks present in coating. Such cracks can cause local
crack related flaking of the coating resulting in early reactions between
the work piece and the cemented carbide. No CVD-cooling cracks are
present in coatings on cermet bodies.

[0040]From Examples 2-4 it is also evident that thicker CVD coatings on
cermet bodies compared to thinner ones result in an increase of the
cutting tool wear resistance.

[0041]It is surprising that, in spite of the known brittleness of cermets,
thick CVD coatings can be used on cermet bodies with strong edge geometry
and thus improve tool wear resistance at high productivity machining
using large cutting depths without edge fracture.

[0042]Although described in connection with preferred embodiments thereof,
it will be appreciated by those skilled in the art that additions,
deletions, modifications, and substitutions not specifically described
may be made without department from the spirit and scope of the invention
as defined in the appended claims.